PS121 Brain & Behaviour Term 1 Part 2 Flashcards
Define Stimulus-Elicited Behaviour
Behaviour produced as an involuntary
and relatively immediate consequence
of sensory stimulation: the behaviour is
a reaction (or response) to a stimulus.
What distinguishes reflexes from other types of stimulus elicited behaviour?
A reflex is a stimulus-elicited behaviour, so the behaviour
itself occurs as an involuntary response to an eliciting stimulus
Define proximal stimulus
Physical energy or
force (electromagnetic, mechanical, acoustic, chemical)
that impinges on sensory receptors and evokes a
change in their membrane potential. Also qualities or
features of this energy, such as a change in level or the
rate of such a change
Define distal stimulus
Distal Stimulus: A perceived/perceptible object,
structure, substance, state of affairs or event in the
environment/body. These are sources or causes of
proximal stimulation (&/or of its features and patterns)
A reflex is a stimulus-elicited behaviour elicted by ______ stimulation
Proximal
True or false the nervous system does not need to identify, recognise or obtain any information about a distal stimulus
True
True or false if the behavioural response is elicited by a distal stimulus,
then the behaviour is not a reflex: it is some other kind of
stimulus-elicited behaviour
True
The Graylag Goose - Egg Retrieval
An egg stimulus acts like a pull of a trigger: once the
response is elicited, the stimulus is no longer required – the
response just carries on
The Releasing Mode of stimulus elicitation
The stimulus triggers the response in a discrete
fashion. The response is ‘stored’ beforehand and the
stimulus releases it. The releasing mode of elicitation,
The Driving Mode of stimulus elicitation
The stimulus drives the response in a continuous
fashion: neural activation evoked by the stimulus is
transformed into efferent signals to the muscles. The
driving mode of elicitation.
Significance of releasing and driving modes
▪ As detailed later, stimulus driven responses vary with stimulus
characteristics – e.g., a strong or intense stimulus evokes a
large response
▪ Driving mode is useful when you want the ‘size’ of the
response to be dependent upon the strength of the stimulus,
Significance of releasing and driving modes
▪ In contrast, stimulus-released responses are independent of
the intensity of the stimulus: the response is the same ‘size’
regardless of the strength of the eliciting stimulus
▪ E.g., the pupillary reflex: as light becomes more intense you
want the pupil to be smaller (greater constriction)
If a response is driven by stimulation, it’s characteristics
follow those of the stimulus:
- Duration: if the eliciting stimulus persists, the response persists
- Amplitude/vigour: if the eliciting stimulus is intense/strong, the response is larger/more vigorous
- Variation: if the eliciting stimulus strength increases and decreases, response vigour increases and decreases
Releasing mode of elicitation is appropriate when…
You want
the size of the response be independent of the stimulus
strength
What does a triangle mean in a diagram at the end of a neuron?
It is an excitatory neuron
What is an arc called that has two interneurons?
Trisynaptic arc, disynaptic arc (if one interneuron) and monosynaptic (if no interneuron)
True or false the phasic stretch is a spinal reflex
true
Define spinal reflex
A reflex with neural circuitry
confined to the spinal cord and the body, the
brain is not involved.
The motorneuron cell bodies lie within the ______ ____
Spinal cord
The sensory neuron cell bodies are in the _____ ____ ______
Dorsal root ganglia that are within spaces formed by the vertebral notches
Type Ia Endings
Are primairly responsive to the speed at which the muscle is getting longer
Type II endings
Are primarily responsive to the amount the muscle has
been stretched (slow adapting properties)
Response strength is measured by?
▪ Response strength is measured by the rate of action potential
propagation, called the firing rate (e.g., action potentials per
second)
Type II response to stimulation
▪ A small stretch
is a weaker
stimulus than a
large one
▪ A sustained (constant) stimulus evokes a sustained
response
▪ Receptors that respond in this way are called slow adapting
receptors
Type Ia response to stimulation
▪ A slow stretch of the muscle is a weaker stimulus than a rapid stretch
▪ A stronger response is evoked by a stronger stimulus
Type 1a response to stimulation
▪ When the length is not changing, there is little response
▪ Receptors that respond in this way are called fast adapting
receptors
Monosynaptic stretch reflex arc
▪ This reflex arc is responsible
for the limb jerk reactions
produced in response to
tendon taps
▪ E.g., if you tap the patellar
tendon, you elicit a knee-jerk
response
▪ Tapping the tendon produces hardly any change in the
length of the (quadriceps) muscles
▪ The change in length is usually less than the thickness of a
hair and is too small to be detected by the spindle afferents
If the muscle isn’t stretched enough
to stimulate the receptors, how can there be a stretch reflex
response?
▪ It’s the 1a afferents that are
involved and the 1a endings do
not respond to the amount of
stretch but to how quickly the
stretch occurs
▪ There is hardly any stretch, but it occurs very fast indeed.
Quickly enough to evoke a large response from the 1a
endings
6 myths about reflexes
- Simple responses: responses are things like blinks, muscle twitches and knee jerks
- Stereotyped responses: performance always involves the same movements and/or muscle contractions
- Mediated by spinal circuits (circuits located in the spinal cord)
- Mediated by reflex arcs: mechanisms are basically chains of neurons (pathways) between sensory receptors and muscles
- Repeatable: the same stimulus always evokes the same response
- Not acquired or modified by learning and experience (because they are innate)
The frog’s wiping reflex
▪ Eliciting stimulus: irritation at a location on the skin (e.g.,
applied using a piece of acid soaked paper)
▪ Response: movement involving extension of rear leg wiping
the ‘toes’ over the stimulus
▪ So foot positioning depends upon
stimulus location
▪ The position to which the foot should be moved
depends upon the position of the forelimb
Conclusion: Frog’s Wiping Reflex
▪ Conclusion: frog’s spinal cord “knows” where the limbs are as
well as where the stimulus is
▪ The frog’s spinal cord deals with the following:
1. Knee or ankle joint immobilized with a cast
2. Ankle weighted with a heavy bracelet
3. Stimulus is on the head and the body bent over
▪ These reflex responses are not fixed sequences of joint
motions or fixed patterns of muscle activations
What does the frog’s wiping reflex prove?
The reflex response is NOT stereotyped. The reflex response is able to achieve the same outcome
(removal of the source of irritation) under different
circumstances (location of stimulus, body posture, body
condition)
All the extra-ocular muscles are driven by motorneurons
located in nuclei within the _______
Brainstem
Medial recti motorneurons located within the oculomotor
nuclei at ________ _______
Midbrain level
Lateral recti motorneurons located within the abducens
nuclei at the _________ ________
Medullary level
Will signals from the left abducens nucleus and right oculomotor
nucleus will move the eyes to the left or right?
Left
Will signals from the left oculomotor nucleus and right abducens
nucleus will move the eyes to the left or right?
Right
Why move the eyes?
To look at things and
to stop retinal images jiggling around too much
We move our eyes so the light can hit the most sensitive part of the eye the fovea
The Vestibular-Ocular reflex
The vestibular organs are the semi-circular cannals
Stimulation of the vestibular organs reflexively evokes eye movements
All of this is in the brain stem
The purpose of the vestibular-ocular reflex is to keep the eyes steady when the head jiggles
When you move your head your eyes stay straight if you remain looking in the same direction
The eyes ______-______ so they stay pointing in the same direction
Counter-rotate
The vestibular organs are used for balance
If vestibular organs are lost balance can be relatively restored.
John Crawford Case Study
John Crawford - lost his vestibular organs - he COULD not read blood pumping through the arteries in the neck made the eyes jiggle enough to make reading very difficult
The Vestibulocolic Reflex and the Cervicocollic reflex
Some animals can only move the eyes by moving their head. They need good reflexes to keep the head steady these are the vestibulocolic reflex and the cervicollic reflex.
Varieties of eye movement
Rapid movements of the eye from one position in the orbit to another are called saccadic eye movements
The joint movement and direction of both eyes are called a conjugate eye movement
Convergent eye movement - when the eyes move closer together towards the nose
Divergent eye movement - when both eyes move further away from the nose
The joint movement of the two eyes in opposite directions is called a disconjugate eye movement
The slow movement of eyes to follow a moving object are called small pursuit eye movements
True or false to make a left eye movement motor neurons in the left lateral rectus and the right medial rectus must both contract seperately
False - To make a left eye movement motor neurons in the left lateral rectus and the right medial rectus must both contract simultaneously.
Saccadic eye movements
To make a conjugate saccade to the left these two nuclei must be activated simultaneously
How can this be done?
Interneurons in the abducens nucleus connect to the contralateral oculomtor nucleus
To make a leftward saccade activating signals are sent to the left abducens
These excite the MNs and also interneurons that carry the signal to the right oculomotor nucleus
Contraction of the two muscles on the left sides of the eyes is NOT sufficient
The muscles on the right sides need to relax
This is achieved by shutting off (inhibiting) excitation of these muscles
The command signal comes from a region in the pons called the _______ _______ ______ ______
Paramedian pontine reticular formation. The PPRF generates a burst of excitation that causes the eyes to move rapidly to a new position (the saccadic movement itself)
The signal from the PPRF is a ‘burst’, once it’s over the situation is back to what it was before the burst
Another signal is needed that holds the eyes in their new position - the holding signal is generated by ______ ______ ________
Nucleus Prepositus Hypoglossi
The holding signal is generated by nucleus prepositus hypoglossi
The NPH contains loops (that feedback the output back into the nucleus)
Because it contains loops, this circuit cannot be described in terms of chains (arcs)
This is the basic circuit for generating the leftwards horizontal saccades (the circuit for rightward saccades involves the PPRF, NPH and NGD)
Reflex saccades involve pathways from the sensory organs to the superior colliculi and then to the PPRF
The _______ ______ are midbrain nuclei that are visible as two bumps on the dorsal surface of the midbrain
Superior colliculi
Visual elicited reflex (horizontal) saccades involve the following pathway:
Retinas > Superior colliculi > PPRF
Voluntary saccades are generated by the same brainstem circuit - the difference is that they are not initiated by a stimulus (so not by a signal from a sensory organ) but by an internally generated ‘act of will’
Originates in the frontal lobes of the cerebral cortex
Frontal cortex > Superior colliculi > PPRF
When you make a voluntary saccade, you most often also turn the head as well
You turn the head and the eyes to look in a new direction
You need to turn the VOR off when you make a voluntary head turn to look in a new direction
In what ways does reflex behaviour change?
1) Response can become more/less vigorous (incl.
faster/slower, more forceful/less forceful)
2) Eliciting stimulus can become more/less likely to
elicit the response
3) Response can more/less effectively produce an
outcome
4) A stimulus can come to elicit a new response
Why does reflex behaviour change?
1) Bodily injury or muscle fatigue: what kinds of
changes are produced?
2) Increases and decreases in physical fitness
or strength: what kind of changes are produced?
3) Learning: what kind of changes are produced?
4) Internal state/mood/intention: what kind of
changes are produced?
Learning occurs as a direct result of experience and results in a _________ _________ change in behaviour
Relatively behaviour
▪ A key element for distinguishing changes due to learning
from those due to factors such as fatigue is that learning
produces changes that are relatively permanent
▪ Fatigue wears off quite quickly whereas forgetting is slow
Define reflex habituation
A learning process that leads to the reduced
responsiveness of a reflex as a result of repeatedly eliciting the
response. It reduces the vigour (strength) of an animal’s behavioural
response to a stimulus over repeated elicitations. Habituation is learning NOT to respond to a stimulus.
What test can be done to distinguishing habituation from fatigue?
Train-rest-test protocol
Two basic outcomes of the train-rest-test
1) In the retention test, the
response vigor is restored
(similar to the start of the
training phase) - restoration of vigour is called spontaneous recovery
2) In the retention test, the
response vigor is not
restored (similar to the end
of the training phase) - conclude that habituation took place - decline in vigour due to learning
Define long term habituation
▪ Effects that last days or more are called long-term
habituation effects
Long term habituation
Long term habituation: a learning process that
produces effects that last for days or months and may
take many repeated sessions on successive days to
establish
Define short term habituation
▪ We know that there are some situations in which the effects
of learning last only a short time (minutes or hours)
Short term habituation: a learning process that
produces effects that typically last less than an hour and
can be established during one session on a single day
How can the effects of short term habituation be distinguished from fatigue effects?
▪ A method exists: it involves a phenomenon known as
dishabituation
▪ This is undoing or reversing an habituation effect by the
presentation of an intense aversive stimulus – a kind of
unlearning
▪ Habituation can be ‘undone’ by presentation of such a
stimulus, but it does not undo the effects of fatigue
▪ Fatigue effects persist after the presentation of such a
stimulus, whereas habituation effects do not
Dishabituation
▪ Dishabituation establishes the existence of short-term
habituation
What is the effect of an aversive stimulus applied following habituation of a reflex?
Reflex responsivness/vigour is restored
Reflex sensitization
Responsiveness and vigour increase after aversive stimulation if it has not previously been habituated.
Aplysia Californica - gill withdrawal reflex
The reflex can be readily habituated and sensitized – the
following video shows the reflex itself and its sensitization
by an aversive stimulus (electric shock)
▪ Sensitization occurs mainly in defensive reflexes, avoidance
reflexes and related reflexes like orienting and startle reflexes
▪ It has the opposite effect to habituation and is responsible
for dishabituation – it can undo the effects of habituation
(more later)
How does reflex sensitization differ from habituation?
(1) It normally occurs more quickly (fewer stimuli needed)
(2) It is non-specific: the effects of habituation are
confined to the elicited response (it is specific),
sensitization affects all defensive, avoidance and related
reflexes
Short and long term sensitization
▪ A single aversive stimulus may be sufficient to produce a
short term sensitization effect that lasts from a few minutes
to a few hours
▪ Repeated sessions separated by several hours (each
consisting of a few aversive stimuli) produce long term
sensitization effects that can last for days or weeks
Dual process theory
▪ Have seen that the two process have opposite effects: the
habituation process reduces reflex responsiveness, the
sensitization process increases it
▪ According to dual process theory, sensitization undoes the
effects of habituation and vice versa (they are opponent
processes)
What is the name for two processes that have opposite effects?
Opponent processes: they act in opposition to each other - what one does the other undoes
Dual process theory (more info)
▪ The theory proposes that the habituation process is always
engaged by an eliciting stimulus, regardless of its nature
▪ The sensitization process may be engaged, but to an extent
that depends upon how aversive or arousing the eliciting stimulus is – the more aversive/arousing the greater the effect of the process
▪ Thus, when an eliciting stimulus is presented, both
processes are engaged
▪ Engagement of the habituation process means that
responsiveness decreases, but simultaneous engagement
of the sensitization process produces the opposite effect
▪ Depends upon which process has the larger effect
Dual process theory - what happens if the eliciting stimulus is non-aversive/non-arousing
▪ If the eliciting stimulus is non-aversive/non-arousing, the
habituation process proceeds unopposed and the
responsiveness of the reflex declines progressively with
repeated elicitations
Dual process theory - what happens if an eliciting stimulus is aversive/non-arousing
If an eliciting stimulus is aversive/arousing, the habituation
process is still automatically engaged, but its effects are
counteracted by a stronger sensitization process and reflex
responsiveness increases progressively with repeated
elicitations
What happens if habituation and sensitization have equal strengths?
Both processes are engaged, but
cancel each other out – reflex
responsiveness does not change
▪ Are there examples of reflexes which do not change in
responsiveness/vigour over repeated elicitations?
Dual process theory
▪ Of course: the pupillary reflex and the vestibular-ocular
reflex are two examples that we’ve encountered
Summary of dual process theory
In summary: sensitization effects occur when the sensitization
process is stronger than the habituation process; habituation
effects occur when the habituation process is stronger; when
the two are equally strong, there is no observable change in
reflex responsiveness/vigour
▪ Dual process theory is also
able to explain results like
this
Dual process theory
Response amplitude
▪ These results are from
repeated elicitations of a foot
withdrawal response in cats
by mildly aversive stimulation
The changes in reflex behaviour (or lack thereof) are a result of the combined effects of the two processes and so
both are part of learning
▪ Without the sensitization process, habituation is not learning
– it is merely a mechanism that reduces responsiveness
regardless of whether the stimulus is worth responding to
Dual process theory
▪ Sensitization and habituation are two process that work
together to produce learning – both are learning processes
Aplysia Gill Withdrawal Reflex
This reflex is mediated by a simple neural circuit involving a
population of about 20-30 SNs, some interneurons and about
10 motorneurons
A brief tickle of the siphon elicits a rapid gill withdrawal. A few tickles repeated with an ISI of no more than about 30 to
40 seconds will quickly habituate the response.
What changes in the gill circuit occur as a result of repeated tickling?
The effectiveness (strength) of
the synaptic connections shown hatched
▪ The synaptic terminals of the SNs release less transmitter
substance in response to the arrival of action potentials - so
less excitatory effect on INs and MNs
▪ This change only happens if the effects of the previous
release of transmitter are present when the next release
occurs (a sort of memory). Explains why short ISI needed
Long term habituation - gill withdrawal response
If sessions of repeated ticklings with short ISIs are repeated
at intervals of a day or so, a long term effect is produced that can last weeks or months. The changes that occur in long term habituation involve
structural changes at the cellular level. ▪ These changes include a reduced number of connections
between one neuron and the next. Regardless of the changes to synaptic connectivity that take
place, habituation effects in elementary reflex circuits are
due to a reduction of the efficacy (strength) of some synaptic
connections within the circuitry
What is the reduced number of connections between one neuron and the next called?
Homosynaptic depression
Neural changes in short term sensitization - gill withdrawal reflex
▪ The presynaptic
connections cause
increased neurotransmitter
release at the ringed
synapses
▪ This increases the strength
of the connections, which
leads to an increase in the
‘strength’ (vigour) of the
withdrawal response
▪ The effect is the exact
opposite of that produced by
short term habituation
Effects of long term sensitization
▪ Long term effects can be produced by a series of sessions
of shock delivery over a few days
Long term effects are associated with structural changes in
the synaptic connections.
▪ These changes include an increased number of
connections between one neuron and the next
True or false dishabituation reverses short and long term habituation
False - ‘Dishabituation’ only reverses the short term habituation
changes
Why is the reduction in stretch reflex amplitude (when someone stands on a tilted platform) is not an habituation effect?
(1) The reduction is only present if the person
continues to stand up. If they sit or lie down, the
response amplitude is back to normal
(2) In a sitting or lying person, 4 or 5 stretches of
the calf muscles produces no change in reflex
response amplitude
(3) The reduction cannot be dishabituated by
presenting aversive stimuli
True or false pavlovian learning is a type of associative learning
True
True or false pavlovian learning can lead to the acquisition of new reflexes
True - Pavlovian learning can lead to the acquisition of new
reflexes (and so refutes the claim that all reflexes are innate
and not acquired as a result of experience)
Give the basic structure of Pavlovian learning
US elicits UR
US and CR combined elicits UR (conditioning)
CS elicits CR
Myths about Pavlovian learnings
1) The CR is the same as the UR.
2) Pairing the US and CS is a necessary condition for
acquiring a CR – i.e., they must occur together if acquisition
is to occur.
3) Pairing the US and CS is a sufficient condition for
acquiring a CR – i.e., if they occur together, then a CR will
(eventually) be acquired.
Standard view of Pavlovian learning
4) The US-UR reflex is a pre-existing, innate reflex; the CSCR reflex is an acquired reflex; so it’s all about reflexes
Debunking CR = UR
▪ Consider conditioning a rat
using foot shock as the US
and a tone or light as the
CS
▪ Electric shock (US) delivered to
the feet of a rat (through the
cage floor) reflexively elicits a
jump (withdrawal reflex
response = UR
▪ Before training the tone alone
(CS) only elicits an orienting
response
▪ During training the CS and US
are paired
CR ≡ UR?
▪ Rats learn to respond to the CS, but the CR is not a
withdrawal response – the rat does not jump or lift its feet
from the floor when the CS is presented
▪ After training, the rat
responds to the CS by
‘freezing’
▪ The CR is a different kind of response – its result is quite
different to that of the UR
Debunking CR=UR - conditional responses to insulin injection
▪ Rat is injected with
insulin (US)
▪ UR = hypoglycemia (a
decrease in blood
glucose level)
▪ CS = stimuli associated with being injected
CR ≡ UR?
▪ Training: injection repeated a number of times at suitable
intervals (sufficiently long for recovery)
▪ The result is that the rat acquires a CR (revealed when the
injection contains only saline)
▪ The CR is the opposite of the UR
▪ CR = hyperglycemia (increase in blood glucose level)
Is the CS-US pairing necessary for acquiring a CR?
If pairing is necessary, then there can be no situations in
which a CR is acquired when the CS and US are not paired
▪ Consider a conditioning procedure in which the US is only
presented if the CS is not presented (no pairing)
▪ Are there any such situations?
▪ If the CS (e.g., tone) is presented, then no US (e.g., shock) is
presented. The US & CS are both presented, but not paired
▪ If CS-US pairing is necessary, predict that no CRs will be
acquired when they are not paired. Is this what happens?
▪ No - CRs can be acquired
▪ When US is aversive, CR = approach to the location of the
CS
▪ When the US is appetitive (desirable/pleasurable ), CR =
avoidance of the location of the CS
▪ The unpaired procedure (if CS then no US) is called an
inhibitory conditioning procedure
What are the four types of CS-US pairings?
Simultaneous conditioning
Trace conditioning
Delay conditioning
Backward conditioning
The most effective for acquisition of CRs simultaneous and delay conditioning.
Does the type of pairing matter?
▪ The eye blink conditioning results are typical
Does the type of pairing matter?
▪ It matters how the CS and US are paired: backwards and
simultaneous conditioning are ineffective as are positive
delays (forward conditioning) that are too short or too long
▪ It is true that conditioning is less effective when the
interval is longer, but only for ‘forward’ procedures (and
very short intervals are ineffective)
▪ If pairing is sufficient, then the only thing that would matter
would be the time between stimuli – the longer the delay
or trace interval, the less effective the procedure
▪ Similar results are obtained using the trace conditioning
procedure, but trace intervals more than 2 or 3 seconds
are ineffective in eye blink conditioning
The effect of delay interval - eyeblink conditioning
▪ What do these results tell us?
▪ First: simultaneous conditioning
is ineffective (0% CRs acquired)
▪ Second: short delays are
ineffective in both backward and
forward directions
▪ NB: backward conditioning has been found to be ineffective
for any length of delay
▪ Positive (forward) delays are most effective between 200 –
400 ms, shorter and longer delays are less effective
▪ NB: positive delays of more than about 5 seconds are
ineffective
See Week 9 Lecture 2
For examples of debunking myths of Pavlovian learning
Pavlovian learning - prediction and anticipation
In Pavlovian conditioning, the anticipated/predicted thing
is called the US and the preceding thing is called the CS
(as both are stimuli)
Rabbits eye blink conditioning
Rabbit in experimental conditions cannot move around had an unchanging view with very little in it. The only changing external stimuli is exposed to the air puff US and tone CS. Acquisition is not a quick process it is a slow process needing over 200 trials for rabbits to be reliably blinking (>50%) in response to the CS.
Pavlovian learning is a process for establishing anticipatory/preparatory responses that works by discovering what stimuli signal significant future events
- Only stimuli that occur before significant events/stimuli that are relevant
- Stimuli that occur both before and after are not relevant
- Only stimuli that occur within the right period of time are
relevant (not too soon and not to long before) - Familiar stimuli are not relevant
What is the term for when an organisms learns to respond to a CS as a result of conditioning if that CS belongs with the US?
CS-US belongingness
Seligmans aversion to sauce Bernaise
▪ Seligman recounted a tale
about how he once ate this
dish in a restaurant
▪ Several hours after eating it,
he fell very ill
▪ Some time later he had sauce béarnaise again, but found
that he couldn’t bear the taste and smell of it, just thinking
about it made him nauseous
▪ He had acquired an aversion to a once loved food and
reports that it was more than 10 years until he could eat it
again
Taste/smell aversions
▪ It is unusual because the CS-US delay can be very long (up
to 6 or 7 hours is most effective, but delays of as much as
24 hours may produce some aversion) and just one
experience may be sufficient
▪ The learning process is easily ‘fooled’ – if you fall sick after
having eaten a novel/strongly/unusually flavoured food/
drink you are likely to develop an aversion to it, regardless
of the cause of your illness
▪ Seligman’s illness was not caused by the sauce (or
anything else he ate) but by gastric flu
Group 1 rats
Would receive a dose of x-rays sufficient to cause radiation sickness (US) and a audio-visual stimulus bright noisy water and tasty water (CS) . Group 1 acquired an aversion to the tasty water but not the bright-noisy water - rats still thirsty were tested with either the audio-visual CS alone or the flavour CS alone the more averse the less they licked.
Group 2 rats
Would receive a foot shock (US) and audio-visual stimulus bright noisy water and taste stimulus tasty water. Group 2 acquired an
aversion to the bright
noisy water, but not the
tasty water
Taste/smell aversions
The flavour CS ‘belongs
with’ the illness inducing
US the audio-visual CS ‘belongs with’ the foot shock US.
Pavlovian learning - in cancer treatment
A cancer patient enters hospital for chemotherapy treatment and they eat a meal at lunchtime
A few hours later they receive their treatment and subsequently feel sick and nausesous
They may develop an aversion to some of the foods they ate at lunchtime
Over repeated chemotherapy sessions, the acquired aversions may extend to many common foods (depending on what they’ve eaten in the previous meal)
It is established that these acquired aversions can contribute to the severe loss of appetite that is a common side effect of chemotherapy (and radiotherapy)
Solution: include as part of the last meal/snack before therapy a strongly flavoured/smelling or novel food/drink therefore preventing aversions to basic food
ANV and cancer
Antcipatory Nausea and Vomiting (ANV)
ANV refers to nausea and vomiting that occurs before any chemotherapeutic agent has been administered to the patient
It has been reported that about 30% of cancer patients receiving chemotherapy experience ANV by their fourth session
A Pavlovian conditioning account of ANV is fairly clear and is known to contribute to the phenomenon
CSs - being in the hospital and adminstration of the drug
CRs - nausea and vomitting
USs - the chemotherapeutic agents
URs: nausea and vomiting
Drug Tolerance
Drug tolerance refers to the finding that over repeated administrations, the effects of a drug get progressively smaller
Behavioural theory of drug tolerance
CR = hyperalgesia (increased sensitivity to pain)
UR = decrease in sensitivity to pain
A compensatory response as it counteracts the analgesic effects of the drug and so acts to maintain pain sensitivity
As the CR develops (increases) over repeated administrations of morphine, so tolerance to the drug develops
Larger and larger doses are needed to produce the same effect
Thus, tolerance to a drug like morphine is in part due to the action of compensatory responses (CRs) elicited by the stimuli (CSs) that accompany drug taking
Thus called the behavioural theory of drug tolerence
Drug overdose - behavioural theory
If the CSs are not present (new situation), the CR will be reduced or absent so the effect of a dose will be greater
This can lead to OVERDOSE
A person used to taking a drug in certain locations develops a tolerance partly due to the CR evoked by a situational stimuli (CSs)
To get high they need a large dose to overcome the effect of the CR
If they take the same dose in unfamiliar circumstances, they may be unable to cope (overdose) since the CR is not elicited
Conditional immunosuppression
Cyclophosphamide was used in a study of conditional taste/smell aversions
The experiments (on rats) involved drinking flavoured water (taste CS) and being dosed with cyclophosphamide (US)
The animals would quickly acquire an aversion to the flavoured water, but by the end of the experiments many became seriously ill and some died
The size and number of cyclophosphamide doses were chosen to be safe so what could have caused their death?
It was found that repeated doses of cyclophasmide led to learned immunosuppression effect (the rats immune system was suppressed for a period in response to drinking the flavoured water)
Conditional immunosuppression would potentially be applied in clinical practice and would offer two benefits:
Avoidance of side effects: drugs with side-effects need only be used until the learned effect is established
Cost savings
Studies show that the strategy could work but it has yet to be implemented
There are some drugs that enhance immune function
Experiments with animals have shown that if such drugs are used as a US, it is possible to produce conditional immune enhancement using similar procedures to those that produce conditional immunosuppression
It has been proposed that conditional immune suppression and enhancement contribute to some instances of the placebo effect
Indeed the CR in these cases is a placebo effect (according to the definition we will develop)
When the patient is presented with the CS alone (e.g the sight of the pill, the prick of a needle - a placebo) there is an actual physical effect (the immune response) that can be beneficial to health
Two different kinds of placebo effects
An objectively measurable effect on the body’s function or condition (e.g patient recovers from a condition more quickly, heals faste etc)
A psychological effect that is not accompanied by any measurable improvement in function or condition (e.g person reports feeling better or having less pain, but there is no measurable change in their physical condition)
Placebo effect in treatment and medication
Thus a person’s history of medication and treatment can act like a Pavlovian conditioning procedure: treatment/medicine (US) is presented in a paired fashion with a variety of other contextual stimuli (CSs) e.g the therapist, a pill, a syringe
It is not fully understood what role CRs play in the placebo effects that have been observed in clinical contexts (usually as part of clinical trials and other research)
In people the problem is that there are always going to be belief and expectancy effects in addition to CRs
Research investigating the relationship between mind, brain and immune function is called psychoneuroimmunology
